神农架大九湖泥炭湿地能量通量及平衡分析

研究大九湖泥炭湿地通量,为准确评估泥炭地生态系统与大气间的物质和能量交换提供基础数据。利用涡度相关系统对神农架大九湖2015年9月～2016年8月的净辐射、显热通量、潜热通量及土壤热通量进行了为期1年的连续观测。结果表明:1)泥炭地全年净辐射为3 146.91MJ/m2,显热通量为931.79MJ/m2,潜热通量为1 762.40MJ/m2,土壤热通量为22.26MJ/m2;能量分配主要以潜热为主,占净辐射的56%。潜热通量为能量散失的主要形式,土壤表现为热汇。2)各能量分量季节变化明显,10月、1月、4月及7月的日变化均以净辐射为基础,呈相似的单峰型曲线变化。3)波文比逐月变化不规律,月平均波文比为0.65、波动在0.34～1.06,年波文比为0.53,全年能量分配潜热通量大于显热通量。4)神农架大九湖泥炭地年能量闭合度为0.86,存在14%的能量不闭合。不闭合的原因可能与下垫面状况、季节变化及平流的影响产生的波动等相关。     

高原泥炭地CO2通量对极端干旱的响应机理研究

[目的]探明极端干旱事件对高原泥炭地二氧化碳(CO2)通量的影响机制。[方法]以若尔盖高原泥炭地为研究对象,采用野外控制实验和静态箱法,利用快速温室气体分析仪测定极端干旱下高原泥炭地CO2通量变化,并结合环境因子及土壤酶活性的测定,分析其变化机制。[结果](1)极端干旱显著降低了若尔盖高原泥炭地生态系统的净生态系统CO2交换(NEE)、生态系统呼吸(Re)和总初级生产力(GPP)(P<0.05)。(2)高原泥炭地生态系统Re对于空气温度和土壤温度的相关性在极端干旱的影响下增强。(3)NEE与β-葡萄糖苷酶(BG)、α-葡萄糖苷酶(AG)显著相关(P<0.05),Re与木糖苷酶(XYL)、纤维素外切酶(CB)显著相关(P<0.05),GPP与BG显著相关(P<0.05)。[结论]高原泥炭地生态系统CO2通量在极端干旱的影响下将显著降低,其对环境因子的相关性也有所增强;NEE和Re变化分别受到不同土壤酶活性的影响,随着土壤深度的增加,与不同深度土壤温度相关性表现出相反的变化趋势。     

Drainage,Liming and Fertilization of Organic Soils. I. Long-term Effects on Acid/Base Relations

Abstract

Long-term changes of the acid/base relations of organic soils after drainage, fertilization and/or liming at three experimental sites—two ombrogenous and one soligenous—in south central Norway are discussed. These sites were drained, fertilized and/or limed in 1953–1956 and sampled in 1991–1992. Drainage at the ombrogelious sites caused: insignificant shifts of pH, higher bulk densities to 40 cm depth, higher ash percentage, higher contents of N and P to 20 cm depth and reduced concentrations of total Ca, K, Mg, Na, A1 and Fe in soil layers deeper than 20 cm. The soligenous site was not effectively drained; despite this, pH dropped about 0.5 unit in the surface and subsurface soil layers of the control plots, while small changes were measured for most other soil variables. The suggested reason for the pH drop is limited sulphide oxidation in the upper 20 cm drained layer. Base saturation at actual soil pH, when all treatments were included, was estimated with good precision by four regressors: pH, extractable Al, extractable Fe and extractable Ca (R²=0.90–0.95). Similar models explained 97–99”” of the variation in base saturation at soil pH=7.0. The lime effects at the properly drained oligotrophic sites were proportional to applied doses; for pH to 40 cm, base saturation to 60 cm, and Ca concentration to 60 cm depth. At the less well-drained soligenous site, effects were limited to the upper 30 cm layer. Both drainage and liming caused higher cation exchange capacities and proper drainage seems to be a prerequisite for the liming effect. Estimated recovery of calcium to 60 cm depth was 64–79% at the ombrogenous sites and 42–46% at the soligenous site.     

模拟水位下降与刈割对高寒湿地土壤氨氧化与反硝化微生物的影响

湿地土壤是温室气体重要的源和汇,认识湿地生态系统氮循环过程有助于预测氮循环对未来气候变化的响应与反馈机制。为探讨硝化作用和反硝化作用对土壤水位变化和刈割的响应机制,依托于2013年在青藏高原东部若尔盖泥炭地南部湿地设置的野外实验,通过在样地周围挖掘不同深度的排水沟模拟水位下降,结合刈割处理,研究水位下降和刈割对泥炭地土壤氨氧化古菌(Ammonia-oxidizing archaea,AOA)、氨氧化细菌(Ammonia-oxidizing bacteria,AOB)和反硝化细菌(Denitrifying bacteria)丰度的影响。2014年7月取样分析结果表明:水位下降显著降低土壤含水量,水位下降与刈割均显著降低土壤呼吸;氨氧化及反硝化微生物功能基因丰度在各处理间无显著差异,但刈割及其与水位下降的交互作用显著影响AOA-amo A与AOB-amo A基因丰度比。刈割处理显著增加AOB-amo A基因相对丰度,但对AOA-amo A基因丰度无显著影响,揭示AOB可能在湿地土壤硝化过程中占主导地位。土壤nir S基因丰度显著高于nir K基因,表明nir S基因对水位下降及刈割的响应更为敏感。随着土壤水位的下降,刈割促进了由AOB主导的氨氧化过程,而反硝化微生物丰度的增加削减了氨氧化产物硝酸盐的积累,继而降低了土壤硝酸盐含量。     

Impeded drainage stimulates extracellular phenol oxidase activity in riparian peat cores

Peat drainage, a common land‐use practice in Europe, has been associated with habitat degradation and increased particulate and dissolved carbon release. In the UK, peatland drain blockage has been encouraged in recent years as a management practice to preserve peatland habitats and to reduce fluvial carbon loss and municipal water discoloration. Drain blockage has, however, been found to increase drain‐water dissolved organic carbon (DOC) concentrations and coloration in the short term. In order to investigate the contribution of changes in extracellular phenol oxidase activity to the increase in water coloration following peatland drain blockage, cores collected from a riparian peatland in North Wales were incubated under impeded drainage conditions. Impeded drainage resulted in the stimulation of peat extracellular phenol oxidase activity and heightened soluble phenolic concentrations, suggesting that changes in extracellular phenol oxidase activity may be a key driver of increases in DOC and water coloration following peatland drain blockage. An increase in peat pH with impeded drainage was also observed that may have contributed to the heightened soluble phenolic concentrations – directly (through effects on solubility) and/or indirectly as a driver of the elevated extracellular phenol oxidase activity.     

Depth of water table prior to ditch network maintenance is a key factor for tree growth response

Abstract

In boreal-drained peatland forests, tree growth is retarded by the gradual deterioration of drainage ditch networks. In order to avoid the development of suboptimal growth conditions, ditch network maintenance (DNM) operations (ditch cleaning and/or complementary ditching) are annually conducted on an area of about 70,000 ha in Finland. The previous studies indicate that the depth of the water table prior to DNM may influence the magnitude of the growth response to DNM. Tree growth does not necessarily increase after DNM at sites with large stand volume and subsequent low water levels due to tree stand evapotranspiration. We investigated how the pre-treatment water table depth (pre-WTD) in late summer relates to the growth of Scots pine (Pinus sylvestris L.) stands after the DNM operation in 12 field experiments. The increase in mean annual volume growth caused by DNM was negatively related to the pre-WTD, with the highest growth response in stands where the pre-WTD was less than 25–30 cm. DNM did not clearly increase stand growth in sites where the pre-WTD was more than 35–40 cm below the soil surface. There was a high variation in growth response to DNM between the water levels from 20 to 35 cm below the soil surface, indicating that factors other than water table depth are also needed as decision criteria for assessing the appropriate timing of ditch network maintenance.     

Biogeochemical impacts of clearfelling and reforestation on blanket-peatland streams: II. major ions and dissolved organic carbon

Streams and drains in blanket-peatland forest in western Ireland were sampled weekly over 5 years, 1996–2000, using continuous, depth-proportional passive sampling. Analysis was for pH, alkalinity by Gran titration, anions by IC, metals by ICP, aluminium speciation by loaded-resin exchange, and dissolved organic carbon (DOC) by absorbance at 320 nm.

Effects of felling are identified graphically from two forest drains whose catchments (both about 1 ha) were clearfelled, and partial clearfelling of one larger catchment (somewhat over 1 km²), in summer 1999. Calcium concentrations and alkalinity were increased in the drain- and streamwater from the felled areas. The pH was increased in drains, while in the larger stream, pH range decreased while the mean increased. Phosphorus increased markedly with clearfell, in the absence of recent fertilising, and also increased with fertilising; these results are reported in an accompanying paper. Ammonium-nitrogen concentrations were increased in the two drains with felling, and temporarily decreased in the larger stream. Nitrate increased in some cases. Potassium and manganese concentrations also increased. Concentrations of DOC and organic monomeric aluminium increased gradually, subject to a continuing strong annual cycle. There were no clearfelling effects on concentrations of solphate, suspended solids or inorganic monomeric aluminium. In the two drains (fully clearfelled), concentrations of sodium, chloride and magnesium, and conductivity, were all reduced after felling. Fertilising effects other than for phosphorus were indistinct.

Effects of the combined clearfell–reforestation treatment were testable statistically, using randomised intervention analysis, between two larger streams (1 km²) as a treatment–control comparison. There were statistically significant positive responses in streamwater concentrations of nitrate, potassium, calcium, DOC and aluminium fractions. The implications for management practice depend on whether the loss of nutrients is sustainable for future crop productivity, and whether critical limits and loads of receiving ecosystems are exceeded.